Contactless gesture-controlled devices recognize and interpret movements of the human body in order to interact with and control these devices without direct physical contact. Traditional gestural input methods, which often require moving a finger, hand, or even an entire arm in mid-air, may induce fatigue over time. Fine-grained, or “micro-gestures,” may introduce relatively less fatigue over time.
However, tracking fine-grained gestures, for example, finger and thumb-tip gestures, remains very challenging due to the small magnitude of digit motions and frequent occurrences of self-occlusion. Existing studies have exploited magnetic sensing, which achieves a relatively high tracking precision but requires fingers to be instrumented with magnets and sensors. Another project, the Google Soli project, explored the use of millimeter-wave radar to sense subtle finger movement without instrumenting the user. The energy consumption of the active sensor in such a system, however, is a concern, especially for small wearable devices, such as smartwatches and augmented reality glasses, among others.